Why does aluminium have maximum covalency of 6 if it has 9 Orbitals in valence shell?

Q. Elements X, Y, and Z have atomic numbers 6, 9, and 12 respectively. Which one has four electrons in its valence shell?

Q. An element has $3^{rd}$ shell as its valence shell. The maximum number of electrons in its valence shell would be

Q. Nitrogen is restricted to a maximum covalency of $4$ since only four (one s and three p) orbitals are available for bonding. The heavier elements have vacant d orbitals in the outermost shell which can be used for bonding (covalency) and hence, expand their covalence as in $P{F}_6^{-}$.

Q. Which of the following elements has 6 electrons in its valence shell?